Microbiologically influenced corrosion (“MIC”) poses severe operational, environmental, and safety problems to the petroleum and/or natural gas industries, particularly with respect to corrosion of equipment used in the storage, processing, and/or transport of oil and gas crude and/or processed materials. Costs resulting from MIC in these industries due to repair and replacement of damaged equipment, spoiled oil, environmental clean-up, and injury-related health care, amount to well over several billion USD per year.
The mechanisms by which microbial influenced corrosion causes damage are poorly understood despite many decades of research. See Kwan Li et al., “Beating the bugs: Roles of microbial biofilms in corrosion, Corrosion Reviews,” Vol. 31, Issue 3-6, December 2013, pp. 73-84 (the contents of which are incorporated by reference). However, it is believed that microbiologically influenced corrosion is primarily caused by the formation of microbial biofilms on equipment metal surfaces that come into contact with produced water associated with crude oil and gas and/or the liquid systems involved in their refinery.
The microorganisms thought to be primarily responsible for corrosion at least in an anaerobic environment within the oil industry are sulfate-reducing bacteria. Other culpable bacteria include iron oxidizing bacteria, sulfur oxidizing bacteria, nitrate reducing bacteria, methanogens, and acid producing bacteria, among others. These categories of bacteria generally are capable of oxidizing metal directly, producing metabolic products that are corrosive (e.g., hydrogen sulfide gas), and/or leading to the formation of biofilms that otherwise alter the local environment thereby accelerating corrosion. See Jack, T. R. (2002) Biological corrosion failures. In ASM Handbook Volume 11: Failure Analysis and Prevention. Shipley, R. J., and Becker, W. T. (eds). Materials Park, Ohio, USA: ASM International, pp. 881-898 and Enning and Garrelfs (2014) Corrosion of iron by sulfate-reducing bacteria—New views of an old problem. Applied and Environmental Microbiology. Volume 80, pp. 1226-1236.
Sulfate-reducing bacteria, are ubiquitous and can grow in almost any environment. They are routinely found in waters associated with oil production systems and can be found in virtually all industrial aqueous processes, including cooling water systems and petroleum refining. Sulfate-reducing bacteria require an anaerobic (oxygen-free) aqueous solution containing adequate nutrients, an electron donor, and electron acceptor. A typical electron acceptor is sulfate, which produces hydrogen sulfide upon reduction. Hydrogen sulfide is a highly corrosive gas and reacts with metal surfaces to form insoluble iron sulfide corrosion products. In addition, hydrogen sulfide partitions into the water, oil, and natural gas phases of produced fluids and creates a number of serious problems. For instance, “sour” oil and gas, which contains high levels of hydrogen sulfide, have a lower commercial value than low sulfide oil and gas. Removing biogenic hydrogen sulfide from sour oil and gas increases the cost of these products. It is also an extremely toxic gas and is immediately lethal to humans at even small concentrations. Thus, its presence in the oil field poses a threat to worker safety.
Corrosion—often characterized in association with pitting of metal surfaces—caused by sulfate-reducing bacteria or other environmental microorganisms frequently results in extensive damage to oil and gas storage, production, and transportation equipment. Pipe systems, tank bottoms, and other pieces of oil production equipment can rapidly fail if there are areas where microbial corrosion is occurring. If a failure occurs in a pipeline or oil storage tank bottom, the released oil can have serious environmental consequences. Also, if a failure occurs in a high pressure water or gas line, the consequences may be worker injury or death. Any failure at least involves repair or replacement costs.
A variety of strategies have been developed or discussed to mitigate the corrosive effects of MIC and/or the biofilms that contribute to or cause MIC. Such techniques include the use of corrosion-resistant metals, temperature control, pH control, radiation, filtration, protective coatings, the use of corrosion inhibitors or other chemical controls (e.g., biocides, oxidizers, acids, alkalis), bacteriological controls (e.g., phages, enzymes, parasitic bacteria, antibodies, competitive microflora), pigging (i.e., mechanical delamination of corrosion products), anodic and cathodic protection, and modulation of nutrient levels. However, each of these existing methods face obstacles, such as, high cost, lack of effectiveness, short life-span, or requirement for repeat applications. Moreover, given the highly unpredictable nature of MIC formation, it is challenging to know just when to administer such treatments, as well as what level of aggressiveness any given treatment should have. A more thorough understanding of the conditions which lead to MIC formation would allow improved MIC mitigation management since treatments could be more localized and selective. This would also lead to significant cost savings as treatments would not be wasted on componentry that lack the conditions conducive for MIC formation.
Thus, there exists a need in the art for an improved approaches for MIC mitigation that facilitate reliable prediction, assessment, and monitoring of MIC conditions paired with treatment programs which are matched to the level of MIC severity.